GI motility + Microbiome Flashcards
Types of GI contractions. Where does each contraction take place?
Propagated : waves of contraction and relaxation; e.g. in peristalsis
Tonic: area of muscle mostly contracted in place so stimulus >> relaxation e.g. sphincters
Segmental: Movement of material back and forth e.g. in colon
Inhibited contraction: gut doesn’t move e.g. “ileus”
Name the GI tract sphincters and what they separate (hint: ULe Oddi’s Py, IV and the anals)
UES: mouth from esophagus
LES: esophagus from stomach
Sphincter of Oddi: pancreatobiliary ducts from duodenum
Ileocecal valve: small intestine from large intestine
Internal and external anal sphincters: under involuntary and voluntary control, respectively
Describe the excitation contraction coupling process in the gut (what happens at rest vs when muscle is stimulated)?
What are the 3 things that control the transmission of slow waves and how do they work? (hint: one = within interstitial cells of Cajal, the other 2 are neurotransmitters)
@ rest: slow waves = baseline membrane potentials; bring membrane potential closer to AP threshold and control frequency and timing of APs
stimulated: increased Ca2+ concentration; AP occurs on top of BER, muscle is contracted
Gap junctions, ACh, NE
Gap junctions (in interstitial cells of Cajal): allow rapid AP transmission (and concerted muscle contraction)
ACh: stimulatory; increases slow wave amplitude
NorEpinephrine: inhibitory; decreases slow wave amplitude
Describe the difference between primary and secondary peristaltic waves. (what stimulates either and what does that mean for the movement of the food bolus?)
Primary peristaltic wave: stimulated by deglutition (food moved down the esophagus but not competely)
Secondary peristaltic wave: stimulated by local esophageal distension (stretch receptors in esophageal lining stimulated by presence of food bolus>>local reflex = distension >> moves food bolus further down esophagus)
Describe the deglutition process (i.e. swallowing). (What are the 3 phases? In which phase do the UES and LES’s relax? What process propels the food bolus down the esophagus?)
Phases: Voluntray/Oral ; Pharyngeal ; Esophageal
Voluntary phase: tongue senses food >> signal received by swallowign ctr in medulla >> tongue pushes food posterior pharynx
Pharyngeal phase: epiglottis folds over trachea to cover it>> upper ES relaxes (lower ES relaxes at beginning of swallowing) >> food bolus moves down esophagus
Esophageal phase: food bolus propelled down esophagus by peristalsis
What type of muscle makes up the proximal and distal esophagus? What are each portions innervated by and what is the effect of this innervation?
Proximal esophagus has striated muscle
Distal esophagus has smooth muscle (circular and longitudinal)
Proximal esophagus innervated by vagal motor neurons w/ cell bodies in nucleus ambiguus; effect = relaxation of upper esophageal sphincter
Distal esophagus innerated by vagal preganglionic neurons w/ cell bodies in distal motor nucleus; effect = relaxation of circular smooth muscle in LES
What is the contribution of the migrating motor complex to gastric motility? What are the phases of the MMC and what hormone stimulates this process? Where is this hormone released and what influences its activity?
MMC stimulates gastric motility during fasting to remove residual food in the gut
Phases:
1: Physiologic ileus - no contraction
2: Intermittent motor activity - some contraction
3: Regular, intense and repetitive contractions
(increased Motilin levels right before Phase 3)
Motilin (secreted by M cells) stimulates this process. Released in the stomach and inhibited by eating
Which area of the stomach has phasic or tonic muscle? Why is this difference necessary for the stomach’s function? (i.e. what’s the difference in their function?)
What is the significance of the pacemaker region in the stomach in stomach contraction? Where is this region?
Fundus and part of the body (upper stomach) - has tonic muscle
Tonic muscle allows for relaxation and distension of the stomach when food enters
Lower portion of the stomach body, antrum, pylorus (lower stomach) - has phasic muscle
When stomach distended, phasic muscle pushes food down the antrum and into the pylorus
The pacemaker region is where the peristaltic waves that push food down the stomach begin and move distally (located in the body of the stomach)
Describe receptive relaxation in the stomach
Swallowing food>> vagus stimulated >> stomach distension >> filling (increases pressure) >> contraction of proximal stomach
What is the contribution of trituration to gastric emptying? Where does this process take place? Over time, what is the rate of emptying of liquids, solids and semi solids (draw a graph to illustrate this)?
Trituration breaks down large particles into smaller substances> Makes is emptying easier and faster
Liquids empty faster than semi solids which empty faster than solids
What changes occur in the duodenum when stomach emptying begins?
Food in duodenum prompts two pathways:
Duodenal cells secrete enterogastrones (Secretin, CCK,GIP) >> slow gastric emptying (slow contraction rate)
Chemoreceptors and stretch receptors activated >> activate enetric neurons to slow gastric emptying (via short reflex); activate CNS >> increases sympathetic activity/decreased parasympathetic activity (via long reflex)
What are the differences in BER and food storage between the stomach and the small intestine?
In stomach: BER = lower half of body going downwards; in small intestine, throughout but faster in the proximal small intestine
Food storage: only in stomach and colon; not in small intestine or esophagus
Contrast the following properties between the small instestine and the large intestine:
Presence of MMC
Retrograde movement
Presence of longitudinal ms
Mass movement of contents
T/F: The BER in the colon facilitates net movement of chyme (i.e. movement of chyme in one direction)
Describe the following contractile patterns:
Mixing
Haustral migration
Mass movement
Falsehood. BER doesn’t facilitate movement of chyme in one direction (there’s a back and forth movement of chyme instead)
Mixing: moves contents short distances in either direction (like segmented contractions)
Haustral migrations: move contents larger distances in either direction
Mass movement: propel contents (by like 20cm or something; happens unidirectionally, after you’ve eaten)
Briefly describe the process leading up to defacation (i.e. what’s the pathway/what reflexes control this process)
Which GI disorder has been most impacted by developments in the human microbiome project? What other GI diseases are being studied in the microbiome project?
C diff infection
IBD, IBS, Obesity and Diabetes
What’s the general makeup of the microbiome? (i.e. which two phylotypes are most abundant? (hint: firm n cute bacteria dates)
What are the 4 other types that are present in low abundance?
Bacteriodetes, Firmicutes
Proteobacteria, Actinobacteria, Fusobacteria, Verrucomicrobia
What are two factors (one happens during birth, the other is something you do for 6 months after birth for baby) influence the kinds of microorganisms that a baby is going to be colonized by?
What bacteria kinds colonize the gut first? Which types colonize next?
Type of birth (vaginal vs C-section)
Formula vs breast feeding
Facultative bacteria, followed by anaerobes
T/F: The adult microbiome fluctuates frequently and bacterial abundance varies greatly over time.
How would you change the gut microbiome?
Falsehood
The adult microbiome stays pretty stable and about 60-70% of the strains don’t change over time. The most stable strains are also the most abundant.
You would have to make a major change in diet/environment
Which parts of the gut have the most bacteria (2 parts)?
Explain the significance of mixing motions in the colon to bacterial growth.
Colon has the most bacteria, distal ileum has the 2nd highest amount of bacteria
Mixing motions in colon provide bacteria more nutrient access, which promotes bacterial growth
What are the metabolic/structural functions of commensal bacteria?
What are the other functions of commensal bacteria? (hint: 2 of the 3 are immune functions)
Epithelial proliferation and generation of SCFAs
Production of antimicrobial peptides; reduction of surface area for pathogenic bacteria; promoting GI motility
Describe 4 ways by which you could alter the microbiome?
Diet
Pre and probiotics (although there’s not enough to suggest the usefulness of this)
Antibiotics
Fecal transplants (helps with C diff infection)
What is the FODMAPS diet and why is it helpful?
What is are the benefits of and one negative consequence of Polyols?
FODMAPS= Fermentable, Oligo-, Di-, Monosaccharides and Polyols
Restriction of FODMAPS = less substrate for gut bacteria to digest and release gas
Benefits of polyols: not metabolized by mouth so that prevents dental carries;won’t raise blood sugar like regular sugar
Con: unabsorbed polyols will be digested by bacteria (produces gas, bloating, etc)
What is the effect of antibiotics on the gut microbiome?
They reduce the # of commensal bacteria as they kill pathogenic bacteria, which changes the microbiome composition, and may have to do with obesity
